UNIVERSITY     OF    CALIFORNIA 

COLLEGE   OF    AGRICULTURE 

AGRICULTURAL    EXPERIMENT   STATION 

BERKELEY,    CALIFORNIA 

CIRCULAR  301 

January,  1926 

BUCKEYE  POISONING  OF  THE 
HONEY  BEE 

G.  H.  VANSELL 


BUCKEYE  POISONING  OF  THE  HONEY  BEE 

Beekeepers  have  long  disagreed  as  to  the  value  of  the  California 
buckeye  {Aesculus  calif ornica  Nuttall)  as  a  honey  plant.  Some  have 
insisted  that  bees  are  killed  by  feeding  on  its  nectar,  while  others  are 
equally  insistent  that  it  is  a  valuable  and  safe  source  of  honey.  This 
divergence  of  opinion  among  honey  producers  can  be  readily  under- 
stood after  studying  the  known  facts  of  the  problem.  A  knowledge 
especially  of  the  peculiar  distribution  of  the  buckeye  and  of  the 
climatic  conditions  governing  its  growth  are  necessary  to  this  under- 
standing. 

A  study  of  the  California  buckeye  in  relation  to  beekeeping,  as 
extended  as  funds  would  permit,  was  undertaken  in  October,  1923. 
Although  the  work  has  not  been  completed,  sufficient  data  are  now 
available  to  give  beekeepers  information  which  will  be  of  value  to 
them. 

Enough  experimental  evidence  has  been  collected  to  show  definitely 
that  wherever  buckeye  is  abundant  it  is  seriously  injurious  to  bees 
during  years  when  a  deficiency  in  top  soil  moisture  exists,  or  when, 
for  any  reason,  other  plants  fail  to  produce  enough  nectar  to  be  more 
attractive  to  the  hive  bee  than  this  plant.  Aesculus  calif  ornica  is  a 
deep-rooted  plant  and  is  not  seriously  affected  by  drought. 

California  buckeye  is  not  found  over  the  entire  state.  It  is  con- 
fined to  a  foothill  zone  extending  around  the  Sacramento  and  San 
Joaquin  valleys  (see  fig.  1).  This  zone  reaches  the  ocean  at  various 
places  from  Mendocino  to  Ventura  counties  and  extends  eastward 
into  the  Antelope  Valley  of  Los  Angeles  County.    The  habitat  of  the 


2  UNIVERSITY    OF    CALIFORNIA- — EXPERIMENT    STATION 

buckeye  varies  greatly  in  different  regions  as  it  depends  to  a  marked 
extent  upon  the  nature  of  the  soil,  direction  of  prevailing  v^inds,  mean 
temperature,  slope,  exposure,  and  other  factors.  In  some  places  it 
is  to  be  found  on  onlj^  one  side  of  a  canon  or  even  only  in  sheltered 
pockets  of  one  side.     There  are  two  districts,  however,  in  which  it  is 


o  u 

I 


M     0    O    0    C      ! 

rr ^ 


X 


N        Y      0     \ 


\ 


\. 


SAN       BERNARDINO 


R     S     t      O     E 


I   IMPERIAL 
I        ^'^1 --^ 

Fig.  1. — The  distributiou  area  of  the  CaHfornia  buckeye  is  roughly  shown 
by  the  lining,  while  the  two  black  spots  indicate  abundance. 


exceedingly  abundant  on  practically  all  exposures.  One  of  these 
extends  from  above  Three  Rivers  in  Tulare  County  into  Kern  County, 
the  other  from  northern  Yolo  County  southward  through  Solano 
and  Napa  counties  (see  fig.  1).     As  is  the  case  with  the  majority  of 


CiRC.  301]  BUCKEYE  POISONING  OF   THE  HONEY  BEE  3 

plants  of  an  arid  or  semi-arid  range,  the  distribution  of  this  species 
is  very  spotted.  This  fact  is  admirably  discussed  by  Coville  in  his 
'' Botany  of  the  Death  Valley  Expedition." 

George  B.  Sudworth  in  his  "Forest  Trees  of  the  Pacific  Slope" 
records  the  occurrence  and  range  of  the  California  buckeye  as  fol- 
lows: "Foothill  and  lower  mountain  slopes;  frequent  on  borders  of 
streams  and  canon  sides  in  dry  gravelly  soils.  Forms  spreading  clumps 
interspersed  with  scrub  oak,  redbud,  occasional  live  oak,  blue  oak, 
gray  pine,  manzanita,  and  other  chaparral  brush ;  largest  in  sheltered 
coves  and  gulches. ' ' 


Fig.  2. — A  pile  of  dead  ''buckeyed"  bees  four  inches  deep  before 
the  entrance  of  a  hive  in  the  Vacaville  district. 

The  blossoming  dates  of  Aesculus  calif ornica  in  different  localities 
vary  from  April  in  the  Winters  Hills  of  Solano  County  to  Septem- 
ber in  the  Santa  Cruz  mountains.  In  warm  dry  areas  the  length  of 
the  blossoming  period  is  about  five  weeks,  while  in  cooler  areas  with 
moist  air  conditions,  the  blossoms  keep  coming  on  for  nearly  three 
months.  Wherever  the  period  is  short,  a  great  many  of  the  blossom 
buds  abort.  Nectar  is  produced  very  freely  in  this  species  throughout 
the  blossoming  period,  and  the  flow  is  not  affected  by  annual  condi- 
tions to  nearly  the  extent  observed  in  shallow-rooted  plants. 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


^^> 


^_ 


-^ 


4i« 


d' 


Fig.  3. — The  bug,  Urhisea  solani  Held.,  whicli  punctures  buckeye  plants.     Bees 
take  up  the  exuding  sap  from  these  feeding  punctures  and  carry  it  to  the  hive. 


CiRC.  301] 


BUCKEYE  POISONING  OF   THE   HONEY   BEE 


Tent  over  buckeye  trees  in  which  bees  were  confined. 
Fig.  4  (above),  inside  of  tent.     Fig.  5  (below),  outside  of  tent. 


b  UNIVERSITY    OP    CALIFORNIA EXPERIMENT    STATION 

The  California  buckeye  is  a  plant  fairly  well  known,  but  a  few 
words  of  description  to  help  those  who  are  not  familiar  with  it  may 
be  given.  Those  who  know  any  of  the  other  species  of  Aesculus  such 
as  the  imported  horse  chestnut  present  in  the  eastern  United  States 
will  immediately  recognize  Aesculus  calif ornica.  It  grows  to  be  a 
tree  of  considerable  size  (40  feet  high)  in  the  southern  part  of  its 
range,  though  in  the  north  it  rarely  attains  a  height  of  15  feet  and  is 
often  bushy  in  growth.  The  bark  is  soft  and  almost  white.  The  leaves 
are  large  (3  to  5  inches  long)  with  five  palmate  stalked  leaflets  of  a 
rich  green  color.  These  drop  from  the  tree  early  in  the  season  and 
over  much  of  its  distribution  area  it  is  almost  naked  by  mid-July.  The 
blossoms  are  very  showy,  occurring  in  a  thyrse  8  to  12  inches  in 
length;  the  individual  flowers  are  white  or  pink  in  color.  When  in 
full  bloom,  the  California  buckeye  is  by  some  considered  one  of  the 
most  beautiful  of  our  American  trees.  The  seed,  which  is  ripened  in 
a  round,  pulpy-green  pod,  is  a  large,  soft-shelled  "buckeye"  from  one 
to  three  inches  in  diameter,  turning  yellow  and  then  brown  at 
maturity. 

As  yet  no  poisonous  substance  has  been  isolated  from  either  buck- 
eye nectar  or  buckeye  honey,  though  undoubtedly  there  is  a  poisonous 
material  present.  It  seems  probable  that  the  material  is  a  very  un- 
stable glucosid.  The  use  of  buckeye  extract  by  the  California  Indians 
for  stupifying  fish  in  rivers  and  lakes  was  once  a  well-known  prac- 
tice. They  also  used  the  seeds  for  food  but  only  after  making  them 
edible  by  roasting  to  remove  the  poison.  The  poisonous  effects  of  the 
green  leaves,  twigs,  and  raw  nuts  upon  children  and  livestock  have 
been  recorded  in  many  states.  During  the  recent  war  Professor  M.  E. 
Jaffa  worked  out  a  satisfactory^  laboratory  method  of  removing  the 
' '  bitter  principle ' '  from  the  nuts  so  that  they  could  be  used  for  grind- 
ing into  food  and  feed  meal,  but  it  never  became  necessary  to  use 
this  material  for  food. 

The  effects  on  bees  of  buckeye  honey,  pollen,  nectar,  and  sap  are 
sometimes  very  severe.  Not  only  the  field  bees,  but  the  adult  queen 
and  drones  are  affected  as  well  as  the  larvae  and  emerging  young 
adults.  In  severe  cases  the  whole  colony  dies  with  the  hive  full  of 
honey.  The  majority  of  the  larvae  being  fed  are  killed  outright  and 
are  in  the  main  devoured  by  the  adults.  Those  young  which  are  not 
killed  will  pupate  and  emerge,  if  they  are  not  so  badly  deformed  that 
they  are  unable  to  do  so.  Adults  with  but  four  normal  legs  are  very 
common.  The  wings  of  practically  all  emerging  young  never  expand. 
Many  of  the  adult  bees  become  weak  and  die  in  the  hives.     They  are 


CiRC.  301 


BUCKEYE  POISONING   OF   THE   HONEY   BEE 


Figs.  6  and  7. — Buckeye  trees  in  full  blossom.     It  was  in  sueli  areas  as  this 
that  some  of  the  investigations  reported  upon  in  this  paper  were  conducted. 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

carried  out  by  the  survivors  and  dumped  in  front  of  the  entrance  in 
a  great  pile  (fig.  2).  Many  of  the  surviving  bees  are  deformed  and 
seem  to  lack  normal  instincts,  for  they  will  crawl  out  of  the  hive  and 
away  from  it,  going  toward  the  sun  and  to  the  tops  of  weeds  and 
grass  to  remain  until  they  die.  The  field  bees  seem  at  times  to  be 
affected  least,  possibly  because  they  are  more  resistant  than  the  larvae. 
However,  nearly  all  of  them  later  become  unable  to  void  fecal 
material  and  they  assume  the  ''shaky"  attitude  of  paralytic  bees.  It 
is  a  common  experience  to  find  an  abnormally  large  number  of  dead 
bees  upon  buckeye  blossoms  in  the  field,  especially  near  the  end  of  the 
flow.  This  may  account  in  part  for  the  small  number  of  affected 
field  bees  sometimes  noted  at  the  hive.  The  queen's  egg  laying  power 
is  cut  down  to  almost  nothing,  a  condition  which  leads  to  attempted 
supersedure.  The  resulting  young  queen  is  often  unable  to  fly  or  in 
case  she  is  able  to  take  the  mating  flight,  she  lays  only  a  very  small 
number  of  eggs.  Arthur  Dickenson,  a  beekeeper  and  queen  breeder 
of  St.  Helena,  states  that  queens  reared  during  buckeye  blossoms  or 
immediately  after  are  never-  any  good  as  layers,  the  great  majority  of 
them  being  drone  laj^ers,  a  fact  which  suggests  lack  of  fertilization. 
Such  drones  as  are  able  to  fly  at  all  are  apparently  weak  in  flying 
powers.  They  do  not  appear  normal  in  any  respect.  In  fact,  with 
severe  poisoning,  the  demoralization  of  all  the  individuals  in  the 
colony  is  often  complete. 

Alfred  Hengst  and  Charles  Steves  have  suffered  heavy  losses  of 
bees  repeatedly  in  the  Three  Rivers  section  of  Tulare  County.  They 
have  at  times  lost  over  half  their  colonies.  In  some  years  apparently 
they  have  to  choose  between  bees  and  no  honey  or  honey  and  no  bees, 
according  to  whether  the  bees  are  left  in  the  valley  or  moved  into  the 
hills  after  fruit  blossoming. 

The  many  cases  in  which  the  effects  of  buckeye  do  not  become 
very  apparent  can  be  explained  in  a  number  of  ways.  Other  things 
being  equal,  the  malady  becomes  increasingly  severe  with  the  greater 
amount  and  the  concentration  of  the  buckeye  products  brought  in 
from  the  field.  When  other  plants  are  yielding  nectar  simultaneously, 
the  bees  gather  their  nectars  and  pollen  and  thus  dilute  the  buckeye 
poison  and  decrease  its  effects.  It  has  been  found  that  heavy  feeding 
of  sugar  syrup  throughout  the  buckeye  flow,  even  where  nectar  from 
other  plants  is  scarce,  brings  about  a  reduction  of  ''buckeye  poison- 
ing." Where  the  rainfall  is  sufficient  or  the  atmosphere  cool  and 
moist  enough  for  abundant  annual  growth  of  mustard,  filaree,  bur 
clover,  sages,  etc.,  the  beekeeper  is  not  bothered  with  this  trouble  to 


CiRC.  301]  BUCKEYE  POISONING  OF   THE   HONEY   BEE 


Fig.  8. — Buckeye  trees  in  blossom.    Looking  out  into  the  Vaca  Valley. 


Fig.  9. — The  major  portion  of  the  trees  on  the  low  hills  in  the  background 
are  buckeyes.     This  shows  how  abundant  they  are  where  conditions  are  favorable. 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


any  extent.  Alameda  and  other  coastal  counties  with  the  ocean  fog 
influencing"  annual  vegetation  and  with  their  comparatively  small 
amount  of  buckeye  are  not  so  subject  to  this  poisoning  as  are  the 
counties  further  away  from  the  ocean  with  dryer  and  warmer  air  and 
soil.     Even  in  an  area  particularly  subject  to  the  effects  the  bees  do 


10  rt 


10  h 


^SK^' 


W^^  m 


11  a 


lib 


Fig.  10,  a  and  h. — Normal  adult  worker  bees.  The  body  of  such  a  bee  is 
very  hairy. 

Fig.  11,  a  and  1). — Affected  field  bees  in  the  hive,  no  longer  able  to  fly. 
They  become  nervous  (shaky)  and  distended  with  a  foul  material  similar  to 
a  dysenteric  condition.  Such  bees  are  picked  bare  of  hair  by  the  teasing  of 
normal  ones  evidently  trying  to  cause  their  departure  from  the  hive. 

not  suffer  nearly  so  much  during  a  wet  year  with  abundant  late  spring 
rains  as  under  the  reverse  condition.  A  correspondence  between  the 
amount  of  buckeye  products  and  the  degree  to  which  the  bees  suffer 
is  evident. 


CiRC.  301] 


BUCKEYE  POISONING  OF   THE   HONEY   BEE 


11 


It  may  be  that  the  buckeye  nectar,  and  pollen  are  not  alone  respon- 
sible. In  many  cases,  perhaps  in  all,  the  bees  actually  gather  buckeye 
sap  together  with  the  nectar  and  pollen.  Mr.  George  J.  Triphon 
(Solano  County),  the  most  extensive  migratory  beekeeper  of  central 
California,  first  called  the  attention  of  the  writer  to  the  occurrence 
of  a  small  plant  bug  Urhisea  solani  Heid.  upon  the  buckeye  twigs, 
leaves,  and  blossoms  (fig.  3).  These  insects,  which  are  normally  grass 
feeders,  migrate  to  the  buckeye  trees  as  the  grass  dries.  They  punc- 
ture the   leaves,  blossom  buds,   and  tender   twigs,   and   from   every 


^. 


12  a 


12  & 


12  c 


12  d 


Fig.  12,  a,  h,  c,  and  d.- — Emerging  '^buckeyed"  bees.  Many  such  bees  are  so 
badly  deformed  that  legs  and  wings  are  useless  to  them;  such  individuals  are 
pulled  from  the  cells  and  thrown  out  of  the  hive.  Others  have  normal  legs 
but  wings  that  never  expand  to  be  of  use  in  flight.  Notice  in  Figure  12  c  the 
clinging  shreds  of  material. 


puncture  a  droplet  of  sap  exudes.  This  sap  is  collected  by  the  hive 
bees  and  may  be  the  cause  of  the  poisoning.  Attempts  will  be  made 
in  the  future  to  collect  enough  of  the  puncture  exudate  in  pipettes 
for  experimental  bee  feeding.  Knowledge  of  the  exact  distribution 
of  this  insect,  coupled  with  knowledge  of  the  constancy  of  this  habit  of 
migration  to  the  buckeye  trees,  may  throw  still  further  light  upon  the 
variation  in  buckeye  poisoning  of  bees  with  differing  localities,  ex- 
posures, rainfall,  temperatures,  etc. 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  accompanying  photographs  show  something  of  how  the  work 
was  carried  on  and  also  the  results  of  the  poison  on  the  bees.  The 
large  tent  frame  (figs.  4  and  5)  was  built  over  a  clump  of  buckeye 
trees  in  which  bees  were  confined.  The  abundance  of  buckeye  in  certain 
areas  is  indicated  in  figs.  6,  7,  8,  and  9.  Some  abnormalities  occurring 
in  adult  field  bees  and  emerging  young  appear  in  figs.  11  and  12. 
Figure  10,  a  and  h,  show  normal  bees  for  comparison. 


Recommendations 

Where  conditions  are  favorable  to  the  development  of  the  malady 
bees  should  be  moved  to  pasturage  where  buckeye  is  scarce  or  lacking 
or  when  practicable  the  buckeye  trees  may  be  cut  out.  Heavy 
feeding  with  thin  sugar  syrup  will  decrease  the  effects  very  markedly, 
but  since  the  blossom  period  is  so  long,  moving  will  ordinarily  be 
more  economical.  The  beekeeper  who  rents  bees  for  fruit  pollination 
in  buckeye  districts  should  be  sure  that  his  bees  are  moved  away  from 
the  district  before  the  buckeye  blossoming  has  progressed  very  far. 
This  is  feasible  because  the  time  betweeen  the  close  of  fruit  blossom 
and  the  start  of  buckeye  allows  ample  opportunity  for  removal.  In 
places  where  the  amount  of  buckeye  is  small  and  other  conditions  are 
unfavorable  for  the  development  of  buckeye  poisoning,  beekeepers 
need  not  worry  about  their  bees  save  in  occasional  abnormally  dry 
years. 

Summary 

The  California  buckeye  has  long  been  accused  of  poisoning  bees. 
Sufficient  data  have  been  compiled  by  experimentation  to  show  that 
this  buckeye  is  detrimental  to  bees  in  various  ways.  The  intensity  of 
the  effect  depends  upon  drought,  heat,  abundance  of  the  species,  etc. 
An  exudation  from  the  feeding  punctures  of  Urhisea  solani  (normally 
a  grass  feeding  bug)  is  also  collected  from  buckeye  by  the  hive  bee 
and  may  contribute  to  the  ''buckeye  poisoning."  Bees  should  be 
moved  away  during  buckeye  blossoming  where  trouble  has  occurred 
or  is  anticipated  in  accordance  with  conditions. 


15?n-l,'26 


